1. Field of the Invention
The present invention relates to a distributor for an internal combustion engine, and more particularly, to a magnetic rotor thereof for generating an ignition timing signal in cooperation with an ignition timing sensor which is disposed in an opposing relation with the rotor. The present invention also relates to a method of producing such a rotor.
2. Description of the Related Art
FIG. 1 shows the longitudinal sectional view of a distributor for supplying a high voltage to the spark plugs of an internal combustion engine. The distributor comprises an ignition timing signal generator which has a rotor of a magnetic material (the top view of which is shown in FIG. 2) and a fixed sensor opposing the rotor. The structure of the distributor is as follows.
The distributor may be divided into a rotating and a static portion. The rotating portion of the distributor comprises: a shaft 1 rotating in synchronism with a crank shaft of the internal combustion engine; a spark advancing sleeve 2 which is rotatably mounted on the shaft 1 and which is driven by the shaft 1 through the intermediary of a centrifugally-operated spark advancing mechanism 3; a reluctor 4 in the form of an ignition timing signal generating rotor of a magnetic material, which is secured to the spark advancing sleeve 2 through a tube 5 of a non-magnetic material which magnetically disconnects the signal generating rotor 4 from the sleeve 2; and a distributor rotor 6 fixedly secured to the spark advancing sleeve 2.. The spark advancing mechanism 3 includes a member 1a fixedly secured to the shaft 1, a pair of centrifugal members 3a, each of which is rotatably mounted on the member 1a by means of a pin 3b and is urged inwardly by a helical spring 3c having one end coupled to the member 1a and the other end coupled to an end portion of a centrifugal member 3a, and a pair of slotted members 3d fixedly secured to the sleeve 2. Each one of the members 3d has a curved slot 3e through which a cylindrical post 3f, which is fixedly secured to an associated centrifugal member 3a, slidably extends so as to allow rotational motion of the centrifugal members 3a with respect to the members 1a , whereby the outward turning motion of the centrifugal members 3a caused by the centrifugal force acting thereon in opposition to the urging forces of the springs 3c brings about relative rotational motion of the slotted members 3d and the sleeve 5 fixed thereto, with respect to the shaft 1 and the member 1a fixed thereto.
The static portion of the distributor comprises: a cup-shaped housing base 7 through which the shaft 1 rotatably extends; a housing cap 8 secured to the housing base 7; an annular cover 9 interposed between the housing base 7 and the cap 8 for partitioning the distributor rotor 6 from the space below; a vacuum-operated spark advancing mechanism 10 secured to the housing base 7; a spark advancing annular plate 10a of the vacuum-operated spark advancing mechanism 10, which is rotatably mounted on the housing base 7 so as to be advanced in rotational angle by the vacuum-operated spark advancing mechanism 10; and an ignition timing sensor 11 which opposes the signal generating rotor 4 and which is fixedly secured to the spark advancing annular plate 10a.
The ignition timing sensor 11 comprises a permanent magnet (not shown) for generating a magnetic flux A passing through the magnetic rotor 4, whereby the non-magnetic tube 5 reduces the leakage flux B to prevent exterior leakage magnetic flux from adversely affecting the function of the sensor 11 and also to enhance the efficiency of the permanent magnet built in the sensor 11. The annular magnetic rotor 4 has a plurality of projections 4a extending in the radial direction from the outer circumferential surface thereof, as shown in FIG. 2. Thus, the reluctance of the magnetic circuit comprising the rotor 4 varies when the rotor 4 rotates with the sleeve 2 in synchronism with the unillustrated crankshaft of the internal combustion engine. The resulting change of the magnetic flux is converted into a voltage signal by a pickup coil (not shown) of the sensor 11 disposed in the magnetic flux. The voltage signal obtained by the pickup coil is utilized to generate an ignition timing signal, by means of which the breaking and making of the current through the primary winding of the ignition coil (not shown) is controlled. The high voltage generated in the secondary winding of the ignition coil is supplied to the distributor rotor 6 through a brush 6a and to the spark plugs of the internal combustion engine in correct sequence through a rotor electrode 6b and a plurality of circumferentially spaced fixed electrodes 8a opposing thereto.
In operation, the spark advancing sleeve 2 rotates with the shaft 1 in synchronism with the crankshaft of the internal combustion engine (not shown) in such a manner that the relative rotational angle of the sleeve 2 with respect to the shaft 1 is advanced by the centrifugally-operated spark advancing mechanism 3 in proportion to the rotational speed of the shaft 1 due to the centrifugal forces acting on the centrifugal members 3a. The rotational or angular position of the timing sensor 11, on the other hand, is advanced by the vacuum-operated spark advancing mechanism 10 which advances the rotational position of the annular member 10a with respect to the housing base 7. Thus, the ignition timing sensor 11 generates the ignition timing signal at the optimum rotational position of the engine crankshaft.
In the case of the above-described conventional distributor, the signal generating magnetic rotor 4 and the non-magnetic tube 5 are produced as separate parts, and are assembled and secured together by means of shrinkage fit, force fit, or a fixing pin. Thus, the conventional signal generating rotor has the disadvantage that it needs a separate part to be mounted on the spark advancing sleeve. This results in an increased number of producing and assembling steps and in an increased difficulty in securely coupling the magnetic rotor to the non-magnetic tube.